Die Messung der Aufeisenung im Trinkwasser – Ein neues Verfahren zur Beurteilung von Deckschichten in schwarzen Stahlrohren

Measurement of iron-pickup by potable water – A new method for the assessment of surface layers in black steel piping Red water in drinking water distribution systems causes problems for the water companies because of the consumers pretension to get drinking water of high quality. The corrosion products in the water are normally iron compounds, which arise from the corrosion process and diffuse through the surface layer into the aqueous phase. With the proposed method, the increase of the iron concentration in the water and parallel the corrosion rate, by the determination of the differential oxygen demand, is measured. This allows to make direct statements with regard to the protective qualities of the surface layer.     

Manufacturing of oxide-dispersion-strengthened steels with the use of preliminary surface oxidation

Regularities of deformation-induced dissolution of a surface layer of iron oxides in matrixes of iron-based alloys with bcc and fcc lattices have been studied by the methods of M?ssbauer spectroscopy, transmission electron microscopy, and X-ray diffraction. A method of producing iron alloys strengthened by dispersed oxide nanoparticles and alloyed with elements possessing a high affinity to oxygen (titanium and yttrium) has been proposed, which implies a dynamic dissolution of a surface layer of iron oxides upon strong cold deformation and a precipitation of secondary yttrium and titanium nanooxides upon a subsequent high-temperature sintering of mechanically alloyed powders. There has been demonstrated a possibility of oxide strengthening of pure iron upon its interaction with air without introducing traditional alloying elements.     

铸铁在青海盐湖卤水中的腐蚀

根据试验结果,分析了灰铸铁在盐湖卤水中的腐蚀特点.由于卤水中盐的浓度很大,盐粒子在试样表面大量沉积.试验结果表明:灰铁在卤水中的腐蚀主要为吸氧腐蚀,出现铸铁的"石墨化"现象.卤水中盐浓度相当于海水盐浓度的十倍左右,这使溶液中氧浓度相对较小,均匀腐蚀率较小.     

An investigation of the influence of physical vapour deposited aluminium layers on the kinetics of organic coating disbondment on iron

A high-throughput method of investigating organic coating delamination from iron substrates incorporating interfacial thin metallic films of varying thickness is presented. Physical vapour deposited aluminium is demonstrated as a means of limiting underfilm oxygen reduction and slowing rates of corrosion-driven cathodic disbondment. A wedge of graded thickness is deposited on an iron surface and over-coated with a model organic layer. After initiating corrosion by applying corrosive electrolyte to a penetrative defect, rates of corrosion-driven delamination are determined by in situ scanning Kelvin probe measurements, enabling the influence of a range of Al thicknesses to be studied on a single sample.     

Review of current research and application of ductile cast iron quality monitoring technologies in Chinese foundry industry

There is a long history of studying and making use of ductile cast iron in China.Over the years,the foundrymen in China have carried out a lot of valuable research and development work for measuring parameters and controlling the quality in ductile cast iron production.Many methods,such as rapid metallographic phase,thermal analysis,eutectic expansion ratio,surface tension measurement,melt electrical resistivity,oxygen and sulfur activity measurement,ultrasonic measurement and sound frequency measurement,have been used and have played important roles in Chinese casting production in the past.These methods can be generally classified as liquid testing and solid testing according to the sample state.Based on the analysis of the present situation of these methods applied in the Chinese metal casting industry,the authors consider that there are two difficult technical problems to be currently solved in monitoring ductile iron quality.One is to seek an effective method for quickly evaluating the nodularizing result through on-the-spot sample analysis before the liquid iron is poured into the mould.The other is to find a nondestructive method for accurately identifying casting quality before castings are delivered.     

Kinetik der mit Wasserstoff- bzw. Sauerstoffdepolarisation verlaufenden Korrosion von Eisen

Kinetics of the corrosion of iron accompained by hydrogen or oxygen depolarisation The paper brings a critical review of research work devoted to the problem of corrosion of iron in aqueous solutions, free from oxygen as well as aerated. The relationship is discussed between corrosion rate on the one hand, on the other hand, the p_H value, the composition of the solution, the admixtures contained in the iron, the structure of the latter, and the condition of the surface of the test specimens. As regards corrosion associated with oxygen depolarisation, the paper also deals with the transport problems. The authors emphasize that the results obtained by different methods are liable to differ from each other.     

Effect of temperature,oxygen partial pressure and calcium lignosulphonate on chalcopyrite dissolution in sulfuric acid solution

The pressure leaching mechanism of chalcopyrite was studied by both leaching tests and in-situ electrochemical measurements. The effects of leaching temperature, oxygen partial pressure, and calcium lignosulphonate, on copper extraction and iron extraction of chalcopyrite pressure leaching were investigated. The leaching rate is accelerated by increasing the leaching temperature from 120 to 150 °C and increasing oxygen partial pressure to 0.7 MPa. The release of iron is faster than that of copper due to the formation of iron-depleted sulfides. Under the optimal leaching conditions without calcium lignosulphonate, the copper and iron extraction rates are 79% and 81%, respectively. The leaching process is mixedly controlled by surface reaction and product layer diffusion with an activation energy of 36.61 kJ/mol. Calcium lignosulphonate can effectively remove the sulfur passive layer, and the activation energy is 45.59 kJ/mol, suggesting that the leaching process with calcium lignosulphonate is controlled by surface chemical reactions. Elemental sulfur is the main leaching product, which is mixed with iron-depleted sulfides and leads to the passivation of chalcopyrite. Electrochemical studies suggest that increasing the oxygen partial pressure leads to increasing the cathodic reaction rate and weakening the passivation of chalcopyrite.     

Weld shape comparison with iron oxide flux and Ar–O2 shielding gas in gas tungsten arc welding

Abstract

The influence of iron oxide flux and O₂–Ar mixed shielding gas on weld shape and penetration in gas tungsten arc welding is investigated by bead-on-plate welding on SUS 304 stainless with low oxygen and low sulphur contents. The oxygen content in the weld metal is measured using a HORIBA EMGA-520 oxygen/nitrogen analyzer. The results show that both the iron oxide flux and the O₂–Ar mixed shielding gas can significantly modify the weld shape from shallow wide to deep narrow. A large weld depth/width ratio around of 0.5 is obtained when the oxygen content in the shielding gas is in the range of 3000–6000 vol. ppm. Oxygen over a certain critical value, i.e. 70 wt. ppm, in the weld pool alters the temperature coefficient of the surface tension on the pool surface, and hence changes the Marangoni convection. A thick oxide layer on the weld pool surface is generated when the oxygen content in the shielding gas is over 6000 vol. ppm, which becomes a barrier for the oxygen conveyance to the liquid pool and prevents the liquid pool from freely moving, and therefore, decreases the intensity of the Marangoni convection on the pool surface.     

Electrochemical properties of iron covered by CVD‐silicon and silicon‐organic molecules

The adhesion of polymeric coatings on iron and steel is interesting especially for industrial applications. Lacquers are important because of their optical properties but also because they protect the metallic surface e.g. from corrosion. The new concept of using adhesion promoters between the polymeric coating and the metallic surface was introduced recently. But the adhesion of polymeric coatings is a difficult task on iron since the surface must be oxide free. This problem can be avoided by covering the iron surface with a thin film of silicon, silicides and SiO₂. Silane molecules chemisorb on top of it and act as adhesion promoters. The silicon reacts with the iron in a CVD process and the silane via a self‐assembly process. We describe the electrochemical properties and the stability of the iron covered by silicon and by silicon‐organic molecules. Impedance and current‐voltage measurements are used for this. The influence of oxygen and nitrogen solved in the electrolyte is described. Also the time dependence of the stability of the surface layer was measured.     

P2O5对熔渣界面氧迁移反应的影响及机理

利用同位素交换法测定了熔渣表面CO2与氧化铁熔渣之间氧迁移反应的速度常数,并基于电化学反应机制,分析了添加P2O5对该过程的影响,建立了一个新的反应动力学模型．该模型认为P2O5作为易挥发组分参与对电子的竞争,抑制氧迁移(CO2 2e=CO O^2-)主反应的进行．对实验数据的分析和拟合表明了模型的可用性,也辅证了反应的电化学机制．     

A fundamental study of Fe-Cr binary alloy-oxide film interfaces at 288 °C by computational chemistry calculations

A quantum chemical molecular dynamics method was used in order to understand the oxide film degradation mechanism at metal/metal-oxide interfaces. The present study shows that oxygen diffusivity in the metal is significantly higher at a Fe-Cr/Fe₂O₃ interface compared to a Fe-Cr/Cr₂O₃ interface. This indicates that Cr₂O₃ enables protection of the surface for a longer period of time than Fe₂O₃ in a high temperature environment. Applied tensile strain enhances the oxygen mobility towards the metal surface. This process helps to increase the oxidation of the metal surface by forming metal oxygen bonds. Atomic charge analysis reveals that the oxygen atoms are negatively charged and the chromium atoms are more highly positively charged than iron ones. The negatively charged oxygen atoms are able to make covalent bonds with the positive metal atoms. This charge transfer process facilitates the formation of metal-oxygen bonds and weakens the metallic bonds.     

The element transfer behavior of gas pool coupled activating TIG welding

This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as the inner layer gas to protect the tungsten electrode and the molten pool metal. Pure O_2,N_2 or mixture of them are used as the outer layer gas to increase the weld penetration and improve the low temperature toughness of weld metal. Through analyzing the interaction between outer gas and arc and the distributions and existing forms of oxygen and nitrogen elements,the transfer behaviors of nitrogen and oxygen from arc to pool were investigated. The results show that,the interaction between the outer gas and arc plasma makes the arc slightly constrict. The incoming oxygen enriches on the molten pool surface and exists in the form of iron oxide,chromium oxide,manganese oxide and silicon oxygen compounds. The incoming nitrogen evenly distributes in the molten pool and exists in the form of nitrogen atom.     

氧电势法炉前快速测定球、蠕化率的研究

为发展一种简便、精确、可靠的炉前快速检测球、蠕化率的方法,综合研究了氧浓差电池的基本原理和变质铁水的溶氧特性,找到了过去通过氧活度测报球化率不准确的原因,同时发现了球化率与氧电势之间有较严格的对应关系,由此发展了氧电势法,并介绍了该法的实施和精确度分析结果。     

Verlauf der Verzunderung und Entkohlung von Eisen-Kohlenstoff-Legierungen in kohlendioxidhaltigem Gas

Scaling and decarburization of iron-carbon alloys in carbon dioxide containing gases The simultaneous scaling and decarburization of iron-carbon alloys in carbon dioxide containing gas was investigated in a closed apparatus at constant volume. In order to obtain continuously available measuring values for the oxidation of iron as well as of carbon, the weight change of the sample and the change of pressure in the reaction volume was measured simultaneously during the experiment. The experimental temperatures were 1000, 1100, and 1200 degree centigrade, whereas the carbon contents amounted 0,196%, 0,33%, 0,48%, and 0,73%. The total oxygen transfer to the sample increased linearly with time in all experiments, the rate constant being the same as in the oxidation of armco iron. The rate of carbon oxidation was determined by the diffusion of carbon in the iron. From these results it was concluded that the total amount of oxygen transferred to the sample is taken up at the outer surface of the scale layer, whereby the phase boundary reaction determines the rate of this oxygen pick-up. A part of the oxygen is consumed for the carbon oxidation, the rest oxidizes the iron. At the phase boundary wustite-iron the oxidation reactions proceed at lasting equilibrium between wustite, iron, dissolved carbon, and the gas phase. The topochemistry of the simultaneous oxidation of iron and carbon at the phase boundary wustite-iron is discussed.     

The Effect of Traces of SO2 on Iron Oxidation: A Microstructural Study

Pure iron has been exposed to pure O₂ and O₂ with 100 ppm SO₂ at 525 °C for 1 and 24 h. The samples were investigated by FIB, SEM, TEM, EDX and EBSD. The oxide scales formed on iron at 525 °C in O₂ and in O₂ + 100 ppm SO₂ are dense and adherent and consist of three layers. The outermost layer consists of hematite. Beneath it there is a duplex-magnetite scale. The two magnetite layers are separated by a straight interface. It is concluded that the inner-magnetite layer grows inward while the outer magnetite layer grows outwards. In the presence of SO₂ the inner-magnetite layer is much thinner, iron sulphate forms at the oxide surface and discrete iron sulphide grains nucleate at the metal/oxide interface. The amount of sulphide at the metal/oxide interface increases with exposure time. The oxidation of iron in oxygen at 525 °C is inhibited by 100 ppm SO₂. The inhibitive effect of SO₂ is attributed to iron sulphate that blocks active sites on the hematite surface, slowing down the formation of oxygen ions. This explains the strong inhibition of the inward growth of magnetite by SO₂. There is also a marked effect on the morphology of the outer oxide, producing hematite whisker growth and a less porous surface in the presence of SO₂.     

Mechanism of Iron Oxide Scale Reduction in 5%H<Subscript>2</Subscript>–N<Subscript>2</Subscript> Gas at 650–900 °C

The reduction behaviour of the oxide scale on hot-rolled, low-carbon steel strip in 5%H₂–N₂ gas at 650–900 °C was studied. In general, the reduction rate of the oxide scale at the centre location was more rapid than that at the near-edge location. In both cases, the reduction rates at 650 °C were extremely low and the rates increased with increased temperature, reaching their maxima at 850 °C. Arrhenius plot of the rate constant derived from the early parabolic stage revealed that the reduction mechanism at 650–750 °C differed from that at 750–850 °C, with the former being oxygen diffusion in α-Fe and the latter most likely iron diffusion in wustite. In all cases, a thin iron layer formed on the scale surface within a very short time and then the thickness of this layer remained essentially unchanged, while the scale layer was gradually reduced via outward migration of the inner wustite–steel interface, as a result of inward iron diffusion through the wustite layer to that interface. More rapid oxygen diffusion through the thin surface iron layer than the oxygen supply rate through interface reaction was believed to result in a lower oxygen potential at the outer iron–wustite interface, thus providing a driving force for iron to diffuse through the wustite layer. The inner wustite–iron interface became undulating initially; then with the rapid advance of some protruding sections, some parts of the wustite layer were reduced through first, and finally the remaining wustite islands were reduced to complete the reduction process. Porosities were generated when wustite islands were reduced due to localized volume shrinkage. Higher oxygen concentrations in the scales of the near-edge samples were believed to be responsible for their slower reduction rates than those of the centre location samples.     

Plasma polymerization – a new and promising way for the corrosion protection of steel

In this paper the glow discharge process is used for the deposition of ultrathin (d>10 nm) plasma polymers on iron specimens. The plasma polymer serves as an interfacial polymeric layer between the passive iron surface and a conventional pigment free water based 1-component primer. Samples were fixed in the grounded electrode of an audio frequency discharge (4 kHz). Cleaning of the iron surface was achieved by an oxygen plasma treatment and plasma polymers were deposited from a mixture of hexamethyldisilane ((CH₃)₃Si-Si(CH₃)₃) and argon. The modification of the surface structure was investigated by the use of quartz crystal microweighing (QCM) and infrared spectroscopy under grazing incidence (IRRAS) as in-situ methods. Both the iron oxide as well as the plasma polymer are characterized in detail by infrared spectroscopy and photoelectron spectroscopy (XPS). The corrosion performance of primer coated samples was tested according to the kinetics of cathodic delamination which was measured in-situ by the Scanning Kelvinprobe (SKP). While the pure oxygen plasma treatment, leading to a contamination free and thickened oxide layer, does not influence the delamination kinetics the existence of an only 5 nm thick plasma polymer at the metal-primer interface leads to a significantly decreased rate of undermining.     

Roughness of the surface layers of plasma oxidation-treated ductile cast iron

The roughness of the surface layers of oxygen plasma-treated ductile cast iron was investigated. The non-intrusive technique of optical emission spectroscopy was used to identify the oxygen plasma species. The etching behaviors at various substrate temperatures in the oxygen plasma treatment were investigated using atomic force microscopy. The etching depth increased first with increasing substrate temperature, and reached maximum depth at 500°C, and then decreased with increasing the substrate temperature further.     

Die Verzunderung von Eisen in O2?SO2-Inertgas-Gemischen bei 900° C

Scaling of iron in O₂? SO₂-inert gas mixtures at 900 °C . Kinetic and metallorgraphic investigations into the oxidation of iron in O₂So₂-inert gas mixtures show, that SO₂ increases the scaling rate of iron when the oxidation in the SO₂ free gas follows a linear kinetic law; in these cases the transport of oxygen from the flowing medium to the specimen surface is the rat-controlling step. Such conditions exist at 900 °C and linear flow velocities of 5.8 cm/s at oxygen contents below about 7% At constant oxygen pressure the constant of the linear kinetic law is a linear function of the SO₂.     

Quantum chemical studies on corrosion inhibition of some lactones on mild steel in acid media

Study of the efficacy of some lactones to counter iron corrosion in 1 M hydrochloric acid using ab initio quantum chemical deductions and its comparison with the available experimental data forms a part of this research. It is believed that the inhibition efficiency has lucid correlation with the charge of oxygen atoms of inhibitor molecules. Furthermore, thermo-chemical calculations for oxepan-2-one (L3) on iron cluster result in adsorption energies close to experimental values. However, the interaction energies of L3 and iron cluster with the natural bond orbital are also reported. Furthermore, interaction energy of hydrogen ion and inhibitor with iron surface is investigated.